The industrial handling of goods, in particular palleted goods requires suitable machines for movement and for storage of these goods. Lift truck vehicles, in particular fork lift trucks with a drivers seat are known and common in the most varied of embodiment forms. The function results in the fact that on receiving and discharging the load of the fork lift truck with the load at the front one must drive frontally onto the respective loading position. The whole device for moving or lifting the load at the same time hinders the view of the driver. Proceeding from this problem the state of the art knows a number of improvements which are aimed at the design of the lift device on the fork lift truck. The lift device consists very generally of a mast mounted in front of the driver's cabin, often designed as a frame-shaped double mast, on which by way of rails or a telescopic device the carrier fork may be vertically lifted. Furthermore on the mast there are mounted the hydraulics required for this or a chain mechanism. The carrier fork consists of end-face surface formed by support members and the horizontal carrier arms or prongs arranged vertically to this, on which the load lies. The carrier fork thus mostly has an L-shape; the vertical end-face surface serves for the fastening on the lift device of the lift mast.
EP 283 637 and DE 296 06 840 describe technical solutions which are aimed at reducing the cross sectional profile of the carrier fork, which lies in the line of vision of the driver. In EP 283 637 there is described the integration into the lift rod of the hydraulics required for lifting the load. The carrier fork with this is conventional, i.e. with the end-face surface upright and fastened on the lift mast transversely to the longitudinal axis of the vehicle. The lift mast is attached on the front side of the vehicle, in front of the wheel axis.
DE 292 06 840 shows an individual lift mast of a small width attached centrally in the front of the vehicle. The inner profile of this serves as a guide rail for a carriage and the carrier fork fastened to the end-face surface.
EP 572 864 suggests a modified arrangement of the lift device. Instead of a conventional fork with a lift device fixedly fastened on the fork lift truck a complicated displacement fork carried via several axes is provided, which a enables lateral loading of the load. With this the actual lift mast is integrated laterally at the front into the carrier fork and thus is removed from the field of view of the driver. Disadvantageous with this is the handling by way of the additional joint axes. By way of the additional lever arms the allowable carrying load is reduced. The lifting height is low.
WO 88/0656 describes a design principle which displaces the lift mast into the rear part of the fork lift truck. The telescopic lift device is designed conventionally with an upright lift mast which however is mounted behind the vehicle cabin and in front of the rear axis of the vehicle. Extendible horizontal transverse carriers connect this lift device to the actual carrier fork which is mounted in front of the driver's cabin in the front of the vehicle. The fastening of the carrier fork on the lift device is effected by the vertically arranged end-face surface of the carrier fork. The viewing impediment to the driver by way of the lift system is alleviated, but not the viewing impediment by way of elements which are attached to the actual carrier fork. Furthermore the system during use does not permit the leaving of the driver cabin. Advantageously the arrangement of the lift mast is in the rear part of the vehicle so that an improved position of the center of gravity with an accommodated load is achieved.
Basically common to all these described solutions is that they do not alleviate the viewing impediment to the driver by way of the vertical end-face surface of the carrier fork, in particular by way of carrier forks with additional devices attached thereto. Such additional devices are above all positioning aids with whose help the arms of the carrier fork may be laterally adjusted relative to the vehicle or by way of which the relative distance of the arms of the carrier fork may be decreased or increased. Such a device in technical jargon is called a fork lateral displacer or prong adjusting means. The positioning means are mostly hydraulically operated, are attached individually or in combination and are integrated together with additional guide elements into the carrier fork, and specifically into the vertical end-face surface. The fork lift trucks known from the sate of the art are chiefly used for the loading and unloading of platform truck transporters (lorries) in warehouses or production facilities. On loading it is exactly at the platform truck height that the view is considerably compromised by way of the standard designs of the carrier fork with a vertical end-face surface, according to the state of the art.